This type of inspecting apparatus is provided with, e.g., a loader chamber in which a wafer as an object to be inspected is conveyed; and a prober chamber for transferring the wafer from and to the loader chamber, wherein the electrical properties of the wafer are inspected within the prober chamber. Provided inside the prober chamber are a mounting table that holds the wafer in place; and a lift mechanism that raises and lowers the mounting table. Further provided within the prober chamber are a probe arranged above the mounting table; and an alignment mechanism that aligns the locations of the probe and the wafer.
In case of inspecting the wafer in the prober chamber, the alignment mechanism is used to align the wafer on the mounting table with the probe. The mounting table is then raised up with the lift mechanism to bring the wafer and the probe into contact with each other. Thereafter, the mounting table is moved up by a specific overdriving amount and the electrical properties of the wafer are inspected while the wafer remains in contact with the probe.
Overdriving the mounting table on this occasion allows the inspection to be performed in a state that the wafer and the probe make contact with each other at a specified contact load. Because of this contact load, a probe card that supports the probe may be bent or the mounting table may be sunk down. For this reason, even if the mounting table is moved up by an exact overdriving amount, the wafer and the probe may fail to contact with each other at a desired contact load.
In view of this, techniques of finding out such a contact load have been proposed in Japanese Application Publication Nos. 2003-050271 and 2003-168707.
First of all, Japanese Application Publication No. 2003-050271 discloses an apparatus for measuring properties of a probe card. This device is adapted to measure the properties of the probe card, which supports a probe, while electrical properties of an object are inspected by raising up a mounting table and bringing the probe into contact with the object on the mounting table. This device includes a load sensor that detects a load applied by the probe card against the mounting table; and a displacement sensor that detects an absolute displacement of the probe card. With this configuration, it is possible to accurately grasp the relationship between an overdriving amount of the mounting table and a resultant load by measuring the absolute displacement of the probe card.
Further, Japanese Application Publication No. 2003-168707 discloses a probe apparatus provided with a contact load monitoring device. The contact load monitoring device is adapted to monitor a contact load by referring to a sinking amount of a mounting table attributable to the contact load applied on the mounting table by a probe during overdriving. Specifically, the contact load monitoring device is provided with a displacement sensor that measures a sinking amount based on a displacement of an undersurface of the mounting table from a reference surface. With this configuration, it is possible to constantly secure the contact load with no deformation of the sensor by monitoring the contact load based on the sinking amount of the mounting table at the time of inspection.
In the meantime, Japanese Patent No. 3128354 discloses an electronic part mounting device. This device includes a head mechanism for holding an electronic part and a head lift mechanism for bringing up and down the head mechanism with respect to a printed circuit board supported by a board lift mechanism. The board lift mechanism is provided with a plurality of supporting pins that supports the printed circuit board. The supporting pins are provided with force sensors that measure a pressing force borne by the respective pins during mounting the electronic part. The operation of the head lift mechanism is controlled by detection signals of the force sensors, so that the electronic part can be pressed against the printed circuit board with a specified pressing force.
However, the techniques described in Japanese Application Publication Nos. 2003-050271 and 2003-168707 are adapted to measure the contact load or the displacement of the mounting table by using a load sensor, such as a load cell or a displacement sensor; and to calculate the relationship between the contact load and the overdriving amount based on the values thus measured. For this reason, when the contact load is applied, the mounting table may be tilted or sunk down, or the sensors may be deformed by the load weight. This may cause to generate an error in the displacement of the mounting table, thereby making it difficult to accurately detect the contact load and to directly measure the contact load.
On the other hand, the apparatus taught in Japanese Patent No. 3128354 makes use of, e.g., a strain gauge or a piezoelectric sensor as the force sensors for detecting the pressing force. In this case, the force sensors need to be provided in multiple numbers on the supporting pins, and the pressing force of the head mechanism needs to be calculated by summing up individual pressing forces applied to the respective force sensors. Further, the forces detected by the force sensors are as small in magnitude as the force required in mounting the electronic part to the printed circuit board, and the influence of individual components' deformation cannot be taken into account.